The present invention relates generally to electron tube architectures and, more particularly, to cathode ray tubes having an evacuated envelope with a display window panel and a reinforcing member attached by thermal shrink-fit methods to the outer periphery thereof.
In recent years, cathode ray tubes (CRTs) have been widely employed as color image display devices in a variety of types of industrial and/or home-use electronic equipment. While other types of display devices, including liquid crystal display (LCD) panels and plasma displays have been developed to date, CRTs still offer enhanced picture image. displayabilities with good resolution. For this very reason, CRTs are adaptable for use as color display devices including, but not limited to, television (TV) receiver sets and monitor units for digital information processing equipment, such as workstations and personal computers (PCs).
One typical prior known CRT is constituted from an evacuated envelope which consists essentially of a display panel, a cone-shaped section known as a "funnel", and a neck. The panel includes a front faceplate having an inner surface on which a phosphor screen is formed. In the neck there is provided an electron gun assembly for generating one or more electron beams, which extend in one plane toward the phosphor screen. The panel and neck are coupled together by the funnel.
The funnel has a deflection device mounted thereon. On the way to the phosphor screen, the electron beams emitted from the gun are deflected across the phosphor screen by means of the deflection device.
The electron gun embedded in the CRT neck is designed to include several electrodes, such as a "cathode", a control electrode, a focus electrode, and an accelerating electrode. After being emitted by the cathode electrode, each beam of electrons arrives at the control electrode, which is responsive to an electrical signal supplied thereto for modulating the electron beam. The modulated beam then travels through the focus electrode and acceleration electrode. When penetrating these electrodes, the beam is given an electromagnetic force so as to be reshaped into a prespecified cross-section. Upon impinging on the phosphor screen, the beam forms a spot thereon. The electron beam, on its way to the phosphor screen, is deflected in the horizontal and vertical directions by means of the deflection device for formation of any desired picture images on the screen.
FIG. 8 schematically depicts in cross-section a typical structure of one prior known CRT of the in-line beam type. As shown herein, the CRT includes a front display panel 1 and a neck 3 which are coupled together by a funnel 2. The panel 1 has a reinforcing metal band 4 around its outer periphery clamped. This band 4 is a generally rectangularly looped strip for use as an implosion protector, and is also known as an "anti-implosion" band in some cases. A phosphor screen 8 is situated on the inside surface of the panel 1. The screen 8 has a large number of phosphor elements luminescing in red, green and blue colors for constitution of an image display screen. A shadow mask 9 acting as a color selection electrode is disposed in front of the inner surface of the display screen 8. The funnel 2 contains therein an inner shield 10 for blocking or shielding any externally attendant magnetic fields. Funnel 2 has a "shoulder" on which deflection yokes 11 are externally mounted for horizontal and vertical deflection of electron beams traveling inside of the CRT. An electron gun 12 is disposed in the neck 3 for emission of three separate electron beams B extending in one lateral plane, in the in-line configuration. The electron gun 12 is operatively associated with a magnetic device 13 for producing color purity correction and beam centering amendment. Additionally, panel 1 is bonded to funnel 2 at a joint or "junction" F providing a sealed environment within the CRT envelope.
In the CRT of FIG. 8, the panel 1 and funnel 2 plus neck 3 make up an evacuated envelope. Electron beams B emitted from the electron gun 12 are electromagnetically deflected in two directions--the horizontal and vertical directions--in the presence of deflection magnetic fields generated by deflection yokes 11 to thereby two-dimensionally scan over the phosphor display screen 8 for visualization of picture images thereon.
To preclude accidental implosion of the CRT, which has an internal vacuum, the tube is typically provided with a reinforcing metal band 4 that is mounted around the outer periphery of the panel 1 for implosion protection. In the CRT shown in FIG. 8, due to its inherent irregularity in shape, the external pressures applied thereto are complicated. It is not simply determinable how great a degree of external pressure acts on which part of the evacuated envelope. FIG. 9 presents a result of analysis indicating a typical distribution pattern of external force components applied to the CRT envelope. As seen from this diagram, the force acting inwardly of the CRT is maximal in strength at or near the "shoulder" of the envelope between the funnel 2 and neck 3, while the force acting outwardly of the CRT is maximal at the outer periphery of the panel 1. Generally, the implosion protective band 4 is clamped around the panel 1 at a location at which the outward pressure is applied, thereby protecting the CRT from implosion.
As shown in FIG. 10, the "anti-implosion" band 4 is designed to have a generally rectangular "closed-loop" shape with four rounded corners when seen from the side of the panel 1 after attachment to the CRT envelope. At the band corners, projected mount plates 14, called "lugs", are provided for suspension and rigid engagement of the CRT with the cabinet of a computer monitor or TV set.
In FIG. 11, there is shown an enlarged partial sectional view of a prior art CRT at one corner of the display panel 1. An anti-implosion metal band 41 is clamped around panel 1, with a glass cloth tape 5 sandwiched therebetween. Dotted line 6 is used to designate a mold match line of panel 1.
Typically the panel 1 consists of a front faceplate, with a slightly "domed" display window having a phosphor screen, and a generally rectangular frame or "periphery" 1P having opposite edges, one of which is bonded to the funnel's rim at joint F of FIG. 8 and the other of which is integrally molded along the mold match line G to the faceplate. The mold match line 6 is observable as a "seam" line on the outer periphery of panel 1, at a location at which the curved screen is abutted at an angle to the panel frame. The mold match section is a portion at which the outer periphery is maximal in the total loop length of panel 1.
Traditionally, the reinforcing band for implosion protection is a generally rectangularly looped flat strip which is rigidly secured to the CRT with the entire strip width being used for clamping. In particular, the band tightly clamps the CRT at or near the mold match portion with maximal compressive strength. The band more tightly clamps the CRT at a certain part extending from the mold match line up toward the screen, as compared to a region spanning from the mold match line to the panel periphery. To accomplish this, the band is made of a flat strip having a folded-back portion, or alternatively a thickness-increased portion, at its one edge on the side extending toward the screen. These portions will be collectively referred to herein as a "curled edge" or more simply as a "flip". The flip is laid out on the outer rounded surface of the screen, whereas a single-plate portion (thickness-reduced portion) of the strip is disposed on the outside walls of the panel frame. The band is bent at the single-plate (thin strip) portion so as to have a "V"-like bent portion 71, which is aligned with the mold match line 6, as shown in FIG. 11, to fit the curved outer shape of the panel 1. This permits the band to be in close contact with the curved panel surfaces.
In the past, the anti-implosion band has been clamped by "thermal shrink-fit" insertion methods. More specifically, the band is heated up prior to attachment to the CRT envelope so that the band thermally expands radially. The heated band is placed around the CRT panel and is then cooled down. The band thus shrinks to tightly clamp the outer periphery of CRT in a direction at right angles to its walls. In FIG. 11, arrow 41a designates the strength of the clamping force at a single-plate portion of the band, while arrow 41b indicates the clamping force at the flip 41 thereof.
As the clamping force 41b on the curved surfaces of the screen is not perpendicular to the panel glass surface and the reinforcing band, this force is vectorially divided into a force component 41c normal thereto and a parallel force component 41d, as shown in FIG. 11. If the CRT envelope with the band attached thereto in this state is subject to thermal processing, then the band can badly behave to move or slip toward the panel front face due to a difference in thermal expansion coefficient between the band 4 and panel 1 in response to the parallel clamping force 41d.
One exemplary slipped band state after thermal processing is shown in FIG. 12. As shown herein, the metal band is moved so that its bent portion 71 is displaced from the mold match line 6 toward the panel front face (upwardly in the drawing). Such slipping of the band causes the band 4 to float at its "free" edge on the side of the CRT neck, resulting in a decrease in the strength of the panel-clamping force of the metal band.
Further, as the slipping of the band increases through successive heatup processes, the lugs 14 of FIG. 10, which are provided at the corners of band 4 for use in mounting the CRT in a monitor or TV cabinet, vary in position accordingly. This lug position variation can result in creation of gap spaces between the CRT and the cabinet. This in turn leads to a deficiency or lack of rigid engagement between them.